Oxygen is one of the essential nutrients that bacteria or fungus requires in an aerobic fermentation process. The oxygen is usually provided by sparging air through a sparge ring in a submerged culture fermentation broth. The sparge ring is often a round metal ring with tens or hundreds of holes drilled on it.
A fermentation broth contains not only biomass, but also carbohydrate such as molasses, corn starch, sugar or corn syrup. Some formulations may also contain vegetable oil as a source of energy and a whole range of minerals and nutrients necessary to keep the biomass healthy.
However, a dense biomass together with the food/nutrients may make the resulting fermentation broth very viscous, which in turn tends to reduce the efficiency of dissolution and transfer of the sparged oxygen to the broth. There is also a potential hazard of having the fermentation broth backing up into the sparger and plugging up some of the holes. Sparger plugging presents a major problem because plugged holes reduce the gas dispersion efficiency. Additionally, the biomass entering the sparger will grow and mutate, resulting in eventual contamination of the fermentation broth.